Vinyl Chloride (CH₂=CHCl)

Vinyl chloride is a reactive gas soluble in alcohol but slightly soluble in water. It is the most important vinyl monomer in the polymer industry. The U.S. production of vinyl chloride, the 16th highest-volume chemical, was approximately 14.8 billion pounds in 1994. Vinyl chloride monomer (VCM) was originally produced by the reaction of hydrochloric acid and acetylene in the presence of HgCl₂ catalyst. The reaction is straightforward and proceeds with high conversion (96% on acetylene):

However, ethylene as a cheap raw material has replaced acetylene for obtaining vinyl chloride. The production of vinyl chloride via ethylene is a three-step process. The first step is the direct chlorination of ethylene to produce ethylene dichloride. Either a liquid- or a vapor-phase process is used:

The exothermic reaction occurs at approximately 4 atmospheres and 40–50°C in the presence of FeCl₃, CuCl₂ or SbCl₃ catalysts. Ethylene bromide may also be used as a catalyst. The second step is the dehydrochlorination of ethylene dichloride (EDC) to vinyl chloride and HCl. The pyrolysis reaction occurs at approximately 500°C and 25 atmospheres in the presence of pumice on charcoal:

The third step, the oxychlorination of ethylene, uses by-product HCl from the previous step to produce more ethylene dichloride:

Ethylene dichloride from this step is combined with that produced from the chlorination of ethylene and introduced to the pyrolysis furnace. The reaction conditions are approximately 225°C and 2–4 atmospheres. In practice the three steps, chlorination, oxychlorination, and dehydrochlorination, are integrated in one process so that no chlorine is lost. Figure 1.1 illustrates the process.

Figure 1.1. The European Vinyls Corporation process for producing vinyl chloride: (1) chlorination section, (2) oxychlorination reactor, (3) steam stripping and caustic treatment of water effluent, (4) EDC distillation, (5) pyrolysis furnace, (6,7,8) VCM and EDC separation, (10)

by-product reactor.